Partially interconnected networks

ABSTRACT

A partially interconnected network has a plurality of topological nodes, each of the topological nodes having at least three direct point-to-point topological links connected to other topological nodes. Each of a proportion of the plurality of topological nodes is connected to one of a group of point-of-presence (PoP) units. The group of PoP units is arranged to provide access to a selected service or services, one or more of each of the at least three direct point-to-point topological links from each topological node not being connected to one of a group of PoP units connecting to one or more than one of the plurality of topological nodes being connected to one of the group of PoP units. There is at least one choice of routing between any two topological nodes, the choice of routing being either via two topological links connected in series at another topological node or a direct point-to-point topological link between the two topological nodes.

The present invention relates to network topologies and in particularPartially Interconnected Network arrangements that are advantageous whenconnecting each main node to the other main nodes.

Reference is made to Patent Application No. GB2363544A and Patent No.GB2350517B, which are imported herein by way of reference.

In Patent Application No. GB2363544A there is described a partiallyinterconnected topological network which has at least six TopologicalNodes, each Topological Node having at least three point-to-pointTopological Links connecting it to some but not all of the TopologicalNodes, there being at least one Choice of routing between any twoTopological Nodes and a Choice of routing is either via twopoint-to-point Topological Links connected in series at anotherTopological Node or a direct point-to-point Topological Link between thetwo Topological Nodes. The topological network is arranged by theapplication of Strongly Regular Graphs and the application of somesymmetric Balanced Incomplete Block Designs.

In Patent No. GB2350517A there is described a partially interconnectednetwork comprising a plurality of Allocated Nodes, which Allocated Nodesare each allocated to one of a number of AREAS, and further comprising aplurality of STAR Nodes (STARs), and also comprising point-to-pointinterconnections between the Allocated Nodes and the STAR Nodes, wherethe number of AREAs with Allocated Nodes connected to an individual STARforms the number of ROUTEs from an individual STAR, the Allocated Nodesof a first of the AREAs being connected to a set comprising some, butnot all, of the STAR Nodes, and wherein further of the AREAs aresimilarly connected to further sets each comprising STAR Nodes and wherethere is at least one connection choice (CHOICE) between any twoAllocated Nodes in different AREAs and where a connection routecomprises two point-to-point interconnections connected in series by aSTAR Node.

Reference is further made to the simultaneously filed application,Patent Application No. GB010234.8, in which is described a partiallyinterconnected network which comprises a plurality of Allocated Nodes,which Allocated Nodes are each allocated to one of a number of Areas(AREAs), and further comprises a plurality of Star Nodes (STARs) andpoint-to-point interconnections between the Allocated Nodes and the StarNodes, where the number of AREAs with Allocated Nodes interconnected toan individual Star forms the number of Routes (ROUTEs) from anindividual STAR, each of a proportion of the plurality of Star Nodeshaving connected thereat one of a group of Point of Presence (PoP)Units, said group of PoP Units being arranged to provide access to aselected service or selected services, the Allocated Nodes of a first ofthe AREAs being interconnected to a set comprising some, but not all, ofthe STAR Nodes, and wherein further of the AREAs are similarlyinterconnected to further sets each comprising STAR Nodes, one, or morethan one, of the direct point-to-point interconnections from eachAllocated Node connecting to one, or more than one, of the plurality ofStar Nodes having connected thereat one of the group of PoP Units, andwhere there is at least one interconnection choice (CHOICE) between anytwo Allocated Nodes in different AREAs and where an interconnectionroute comprises two point-to-point interconnections interconnected inseries by a STAR Node.

The present network is directed towards the connection of a network of“Points-of-Presence” (PoP). A PoP is a unit used to connect, among otherthings, to the Internet. Many Internet Service Providers (ISPs)advertised 90% (or greater) local call coverage in the UK, whichoriginally meant that they have PoPs all around the country which can beaccessed for the cost of a local telephone call. More recently bydialing one network telephone number and with the use of IntelligentNetwork call control arrangements, the network will attempt to choosethe nearest or most accessible PoP available.

For the present invention, the PoPs or Content Servers, may be ISPs,Video Servers, Call Centres, International Network InterconnectionPoints, Further Network Connection Points, which may be accessed withthe help of Intelligent Network call control arrangements and similarfeatures which it is intended should be readily accessed locally as ispractical by subscribers.

According to the present invention there is provided a partiallyinterconnected network having a plurality of Topological Nodes, eachTopological Node having at least three direct point-to-point TopologicalLinks connected to other Topological Nodes, each of a proportion of theplurality of Topological Nodes having connected thereat one of a groupof Point-of Presence (PoP) Units, said group of PoP Units arranged toprovide access to a selected service or services, one or more than oneof each at least three direct point-to Point Topological Links from eachTopological Node not having connected thereat one of a group of PoPUnits connecting to one or more than one of the plurality of TopologicalNodes having connected thereat one of the group of PoP Units, therebeing at least one Choice of routing between any two Topological Nodes,a Choice of routing being either via two Topological Links connected inseries at another Topological Node or a direct point-to-pointTopological Link between the two Topological Nodes.

The present invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIGS. 1 to 5 illustrate various basic networks;

FIG. 6 illustrates the terms used herein and in various mathematicalbooks and treatises;

FIGS. 7 to 9 show a number of further networks;

FIG. 10 lists a range of square networks;

FIG. 11 illustrates a network having a group of Content Serversimplemented;

FIG. 12 illustrates a network having two groups of Content Serversimplemented;

FIG. 13 illustrates a network where the number of Content Servers hasbeen reduced, but still providing cover for all the nodes;

FIG. 14 is a redrawn version of FIG. 12;

FIG. 15 shows the table corresponding to FIG. 14;

FIG. 16 illustrates some of the above figures when constructed using anumber of simple transmission rings;

FIG. 17 illustrates a 10-node network;

FIG. 18 is a redrawn version of FIG. 17;

FIG. 19 is a similar figure to FIG. 18;

FIG. 20 lists the smaller intersecting line networks; and

FIG. 21 lists some Strongly Regular Graphs.

Although many classifications of patterns have been identified, severalexamples of just one particular classification will be used to explainsome relevant Partially Interconnected Networks for connecting CoreNodes together as they are some of the simplest to understand, althoughnot necessarily the most efficient.

Nodes which are connected together to form a full mesh are classified asa two stage network, and it is well known that these can easily blockwhen the balance of the loading (on a near fully loaded network) issignificantly changed. The number of links can also be rather large asit equates to N(N−1)/2 where N is the number of Nodes.

Instead of all the Nodes in a network being connected to each other toform a full mesh, it is possible that a node is directly connected tojust some of the other nodes. Consequently when data has to be passed toa terminating node to which the originating node is not directlyconnected, then the data has to transit via one of the other nodes.However it will be shown that for a Video Centric Network the trafficcan be arranged so that it is not necessary to have to transit viaanother node, provided that an appropriate Regular PartiallyInterconnected Network topology is employed.

For example, FIG. 1 shows a network of 16 nodes, where each node isconnected to just 6 of the other 15 nodes. Node 1 is directly connectedto nodes 2, 3, 4, 5, 9 & 13. The figure also shows the connectivitytable for this network.

In order to reach any of the 9 nodes to which node 1 is not directlyconnected, then it is necessary to transit via one of the other nodes.

FIG. 2 shows two ways of reaching node 7 from node 1. One route is bypassing via node 3 and the other is by passing via node 5. There arejust two ways of transiting via a single other node in this case. Infact there are always just two ways of transiting via a single node whengoing between two nodes which are not directly connected together. Thisregular characteristic is largely because of the regular nature of thestructure.

Of course sometimes, in a practical situation, the direct link betweennodes may be unavailable or overloaded and an alternative is required.

FIG. 3 highlights the direct link between node 1 and node 4. It alsohighlights the two alternative ways of reaching from node 1 to node 4 bytransiting either via node 2 or via node 3. Again because of the regularnature of this network there are always just two alternative ways ofreaching from one node to another node which are directly connected bytransiting via just one other node.

Nodes 1, 2, 3 & 4 are each directly connected together to form a smallmesh, as are nodes 1, 5, 9 & 13. In fact there are 8 such small meshesin the network

FIG. 4 shows each of the 8 meshes as a straight line, and hencesimplifies the diagram. This will enable more complex diagrams to bedrawn without them being too cluttered. Each complete horizontal orvertical line represents a complete Mesh of 6 links between 4 Nodes.

FIG. 5 has 4 extra lines (the wavy lines) added each representing 4additional mesh structures. Each node is now directly connected to 9nodes. By adding the extra connectivity more choices of routes arepossible. There are now 6 choices for reaching from node 1 to node 7 vianodes 2, 3, 5, 6, 11 & 13: and there are 4 alternative choices forreaching from node 1 to node 4, via nodes 2, 3, 5 & 16 in addition tothe direct link. Each complete horizontal, vertical or wavy linerepresents a complete Mesh of 6 links between 4 Nodes.

FIG. 6 explains the terms, including Choices, used in this descriptionand the corresponding mathematical terms, such as are used in “The CRCHandbook of Combinatorial Design”, C. J. Colbourn and J. H. Dinitz(Eds.), CRC Press, Boca Raton, Fla., 1966.

16 is a perfect square and similar characteristics apply to otherperfect squares, such as 25.

FIG. 7 shows 25 nodes each connected to 8 other nodes, with 2 Choicesfor indirect paths and a total of 4 choices between directly connectednodes. The figure also shows the connectivity table for this network.Each complete horizontal or vertical line represents a complete Mesh of10 Links between 5 Nodes.

FIG. 8 again shows 25 nodes, but now with each connected to 12 othernodes, with 6 Choices for indirect paths and a total of 6 choicesbetween directly connected nodes. The figure also shows the connectivitytable for this network. Each complete horizontal, vertical or wavy linerepresents a complete Mesh of 10 Links between 5 Nodes.

FIG. 9 a shows 36 nodes each connected to 10 other nodes, with 2 Choicesfor indirect paths and a total of 5 choices between directly connectednodes. FIG. 9 b also shows another 36 nodes, but now with each nodeconnected to 15 other nodes, with 6 Choices for indirect paths and atotal of 7 choices between directly connected nodes. Each completehorizontal, vertical or wavy line represents a complete Mesh of 15 Linksbetween 6 Nodes.

FIG. 10 lists the characteristics of a range of perfect square networkswhere at least two patterns can be drawn for each value of N, where N isa square of an integer number.

Various growth methods have been investigated and one is by adding a rowof nodes. This is initially very straightforward, but some reconnections(of the diagonals) for the patterns with 6 Choices of indirect pathsoccur when adding a column of (N+1) nodes. Having added a row of N nodesand a column of (N+1) nodes the pattern is the next perfect square up,and the growth process could start again.

Because of the regular nature of the perfect square patterns it ispossible to further exploit their characteristics for Video Centric typeapplications. So that the diagram is not too large the following will beexplained using a 25 node network. It is clearly not practical to haveall content available at all nodes. It is also not desirable to have totransit via another node in order to reach the content of another node.

FIG. 11 shows Replica “A” Content Servers attached to just 5 of thenodes, namely nodes 5, 9, 13, 17 & 21. The same content is directlyavailable at each of those 5 nodes.

Remembering that a line represents a small fill mesh; then for each ofthe other 20 Nodes there is always a direct path to exactly 3 of theReplica “A” Content Servers. This is highlighted for Node 2 which isdirectly connected to nodes 5, 17 & 21 which each have a Replica “A”Content Sever. A further set (or sets) of Replica Content Servers can beadded.

FIG. 12 shows a second set of Content Servers namely Replica “B” whichhave been attached to nodes 3, 7, 11, 20 & 24. By attaching Replica setsof Content Servers in a complementary manner to the PartiallyInterconnected Network, some very effective structures can be achieved.

By using Partially Interconnected Networks the choices of routing aredeliberately restricted. This has advantages, as too many alternativeroutes leads to thinner routes, more transmission systems, more switchports used and longer path hunting times. Regular PartiallyInterconnected Networks are much easier to dimension especially whenallowing for the extra capacity needed to cover for the non availabilityof some of the equipment. The loss of a link or a node is very easy tosimulate and the effect is much the same regardless of which link islost, especially if all the links have similar characteristics. Whenfaults, or unusual events occur the effect of spreading the extra loadwidely and quite uniformly across the rest of the nodes is a fascinatingfeature of Regular Partially Interconnected Networks. Appropriate pathselection algorithms may be chosen in order to minimise the risk ofoverloading links.

FIG. 13 shows that it is possible to obtain cover of all the nodes in a5×5 Node network having just 3 PoPs of Content Servers:

-   -   4 Nodes without a PoP are directly connected to 3 Nodes with a        PoP;    -   6 Nodes without a PoP are directly connected to 2 Nodes with a        PoP;    -   12 Nodes without a PoP are directly connected to 1 Node with a        PoP.

To indicate which Nodes are connected to which PoP or PoPs, each Nodehas an indicator on its circumference at the position of Content ServerX on Node 11, Content Server Y on Node 3 or Content Server Z on Node 19,as appropriate. This arrangement does not give a regular distribution ofconnections and makes provisioning for fault and overload conditionsmuch less efficient. This example has nodes connected to 12 other nodes.In FIG. 7, where the nodes are connected to only 8 others, the fulldiagonal of 5 Content Servers would be required to give all nodeswithout a Content Server access to a node with a Content Server.

FIG. 14 is a redrawn version of FIG. 12 with the Content Serversarranged in horizontal groups, but with the numbering of the 25 nodes inthe same positions, this results in the lines, which represent meshes,being rather cluttered.

FIG. 15 shows the table corresponding to FIG. 14 which has 5 blocks of5×5 without any entries. This is because a group of Content Servers donot need direct connections between them. Hence one of the advantages ofthis network structure is that such connections do not exist. Groups ofContent Servers are arranged horizontally. There are no directconnections between the nodes hosting a group of Content Servers.

Another possibility that results from the regular nature of thedescribed Partially Interconnected Networks, is the exploitation of thefact that the overall network is constructed from several small meshnetworks. It is possible to use a transmission ring as a means ofproducing a small mesh network. For example a 4 node ring carrying 6wavelengths can be used to create a full mesh between the 4 nodes.

FIG. 16 is very similar to some earlier figures, but it has been drawnso as to highlight the possibility of it being constructed from 8 simpletransmission rings. The rings being; 1,2,3,4;

-   -   5,6,7,8;    -   9,10,11,12;    -   13,14, 15,16;    -   1,5,9,13;    -   2,6,10,14;    -   3,7,11,15;    -   4,8,12,16.

All the Partially Interconnected Networks described here could beconstructed this way provided ring limits are not exceeded. The large100 node network would need 30 rings each of 10 nodes and 45 wavelengths(if using WDM).

Other network types, which are not based on perfect squares, can also beused.

FIG. 17 is a 10 node network, where each node is connected to 6 of theother nodes. Nodes 5, 6, 7 & 2 are connected together as a small mesh,as are 4 other groups of 4 nodes.

FIG. 18 is the same as FIG. 17 except that each of the 5 small meshes isshown as a line. This network can be described as an intersecting linenetwork.

FIG. 19 is a similar figure to FIG. 18 except that instead of 5 linesthere are 7 lines, with each line representing a mesh. The connectivitytable is also shown.

FIG. 19 could have a Group of Content Servers attached to nodes 1, 2, 3,4, 5, 6 and 7. This results in all the other 14 nodes being able toaccess 4 of these Content Servers via direct connections. Other groupscould be attached to Nodes 8, 9, 10, 11, 12, 13 and 14 and Nodes 15, 16,17, 18, 19, 20 and 21. Unlike the Perfect Square Networks, withIntersecting Line Networks there are some direct connections, betweenNodes with Content Servers of the same Group.

FIG. 20 lists the smaller Intersecting Line Networks with MultipleChoice SRGs based on intersecting lines with μ=4.

Strongly Regular Graphs (SRGs) are a suitable way of defining aconnectivity pattern for Partially Interconnected Networks with multipleNodes. Some further multiple choice SRGs that are known to be able tohave PoPs attached in a regular manner are listed in FIG. 21.

1. A partially interconnected network, comprising: a plurality oftopological nodes, each topological node having at least three directpoint-to-point topological links connected to other topological nodes,some, but not all, of the plurality of topological nodes havingconnected thereat one of a group of point of presence (PoP) units, saidgroup of PoP units being arranged to provide access to a selectedservice or services, one, or more than one, of each of the at leastthree direct point-to-point topological links from each topological nodenot having connected thereat one of a group of PoP units connecting toone, or more than one, of the plurality of topological nodes havingconnected thereat one of the group of PoP units, and at least one choiceof routing between any two topological nodes, the choice of routingbeing either via two topological links connected in series at anothertopological node or a direct point-to-point topological link between thetwo topological nodes, there being no direct connection between the PoPunits in said group of PoP units.
 2. The partially interconnectednetwork as claimed in claim 1, wherein each of a proportion of theplurality of topological nodes has connected thereat one of a furthergroup of PoP units arranged to provide access to a further selectedservice or further selected services, one, or more than one, of each ofthe at least three direct point-to-point topological links from eachtopological node not having connected thereat one of a further group ofPoP units connecting to one, or more than one, of the plurality oftopological nodes having connected thereat one of the further group ofPoP units.
 3. The partially interconnected network as claimed in claim2, wherein at least one of the selected service, services, furtherselected service and further selected services is chosen from aninternet service provider (ISP), a video source, a call center, aninternational network interconnection point, a further networkinterconnection point, or an intelligent network server, any of which isaccessible with the help of intelligent network call controlarrangements.
 4. The partially interconnected network as claimed inclaim 1, wherein all the topological nodes not having connected thereatone of a particular group of PoP units are each directly connected viadirect point-to-point topological links to an equal number oftopological nodes having connected thereat one of that particular groupof PoP units.